When a surfactant solution is injected into a reservoir previously waterflooded, the residual oil trapped as discontinuous ganglia is mobilized and eventually bunched together forming an oil bank. The aim of this study is to explain the formation of this bank during such a drive. The results of experiments performed in micromodels of glass beads show that: a) Overall recovery can be correlated with the capillary number, Nc = uVfd/O, in which u and Vfd are the viscosity a and Darcy velocity of the injected fluid and O is the interfacial tension with the oil in place. b) Ganglia velocity varies differently with u, Vfd and O, and it tends towards the same limit faster than the velocity of the injected fluid for high values of the capillary number Nc. c) The oil bank is formed only in the case where globule velocity attaints that of injected fluid. the dispaced oil then remains bunched, with high saturation at the level of the surfactant front